1. Field of the Invention
This invention relates to a bicycle wheel rim, more particularly to a bicycle wheel rim which has an enhanced strength to resist impact applied on tire retaining walls thereof and which can be made using a simplified manufacturing process.
2. Description of the Related Art
A conventional bicycle wheel rim is generally produced by forming a metal strip, such as from extruded aluminum, cutting and bending the metal strip to form an annular shape with a predetermined size, and bonding two opposite end portions of the metal strip to form an annular frame. FIG. 1 illustrates the cross-section of the conventional bicycle wheel rim 1 which includes spaced left and right tire retaining walls 11, and an annular spoke mounting wall 12 interconnecting radial inner edges of the tire retaining walls 11. However, the bicycle wheel rim 1 does not have a sufficient strength, especially when it is used for a racing bicycle.
FIGS. 2 and 3 illustrate another conventional bicycle wheel rim 2 which includes left and right tire retaining walls 21 for retaining a bicycle tire 26 therebetween, a spoke mounting wall 22 interconnecting radial inner edges of the tire retaining walls 21, and a reinforcing wall 23 interconnecting the tire retaining walls 21 and disposed radially and outwardly of the spoke mounting wall 22. The spoke mounting wall 22 is formed with a plurality of spoke mounting holes 221 for mounting spoke fasteners 244 thereon. The reinforcing wall 23 is formed with a plurality of through holes 231 which are larger than and which are aligned with the spoke mounting holes 221, respectively, to permit extension of the spoke fasteners 244 therethrough. To mount spokes 243 on the wheel rim 2, a plurality of sockets 25 are required. The sockets 25 are disposed in the wheel rim 2 between the through holes 231 and the spoke mounting holes 221 to guide insertion of the spoke fasteners 244 into the spoke mounting holes 221. A bicycle tire 26 is then installed on the wheel rim 2 by retention between the tire retaining walls 21. Since the reinforcing wall 23 is formed with through holes 231, the bicycle tire 26 generally includes an inflatable inner tire body 261 and an outer tire member 262 enclosing the inner tire body 261. In order to protect the inner tire body 261 from being damaged by peripheries of the through holes 231, a lining 263 is provided around the reinforcing wall 23 for lining the inner tire body 261.
Although the wheel rim 2 is provided with a reinforcing wall 23 to result in an increased strength, the wheel rim 2 suffers from the following drawbacks:
(1) During manufacture, through holes 231 and spoke mounting holes 221 should be formed by punching the reinforcing wall 23 and the spoke mounting wall 22, respectively. Since the through holes 231 and the spoke mounting holes 221 have different sizes, the punching process is relatively complicated.
(2) During assembly, each of the sockets 25 is extended through an aligned pair of the through holes 231 and the spoke mounting holes 221. Then, each of the spoke fasteners 244 is extended into the sockets 25 and is retained therein for fastening a respective one of the spoke 243 thereon. The assembly procedure is both time and labor-consuming, and is uneconomical. Moreover, the sockets 25 must be formed to suit the sizes of the through holes 231 and the spoke mounting holes 221 and the distance between the same. Formation of the sockets 25 thus increases the manufacturing costs for the bicycle wheel rim 2.